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In Auto Making, Lasers Take the Lead

Photonics.comMay 2011
AACHEN, Germany, May 20, 2011 — Automotive manufacturers are looking to lasers for more efficient and economical production methods. Lasers are being used to join, drill, structure, cut and shape various materials to reduce weight and friction while streamlining the production process.

To reduce weight and thereby energy costs, manufacturers increasingly are turning to fiber-reinforced plastics, which are 30 to 50 percent lighter than metal. The problem is that these new materials are difficult to process. Fiber-reinforced plastics are brittle, which means the cutting and drilling tools are quickly worn out, and the conventional assembly techniques used for metal components are often not suitable.

"Lasers represent an ideal alternative here," said Dr. Arnold Gillner of the Fraunhofer Institute for Laser Technology ILT. "Lasers can cut fiber-reinforced plastics without wear and can join them, too. With the appropriate lasers, we can cut and ablate components with minimal thermal side effects. Lasers also can be used for welding lightweight components — a viable alternative to conventional bonding technology. We can even join fiber-reinforced plastics to metals with laser welding. The laser roughens the metal surface, while the plastic, briefly heated, penetrates the pores of the metal and hardens. The results are very stable."

Aluminum and copper battery lugs are welded with a disk laser for the production of battery systems used in electric vehicles. (Image: Fraunhofer ILT)
Weight reduction also can be achieved with high-strength metallic materials. These, however, are difficult to process. "Joining combinations of various materials allows us to make optimal use of the individual materials' specific properties. But this proves to be difficult in many cases," said Dr. Anja Techel, deputy director of the Fraunhofer Institute for Material and Beam Technology IWS. "With our newly developed integrated laser tools, we can now even weld together combinations of materials, free of fissures or cracks."

At Laser World of Photonics 2011 in Munich (May 23 to 26), Fraunhofer scientists will for the first time present a new welding head capable not only of focusing with extreme precision but also of moving back and forth across the seam with high frequency to mix the molten materials. When they harden, they create a stable bond.

Lasers also are saving time and money in tool design. The molds used in the production of plastic fixtures and steering wheels, for example, have to be structured to give the finished component a visually and tactilely appealing surface. Most car manufacturers order a design from their suppliers, whose surface typically has the appearance of leather. Until now, the negative pattern used to create the design has been etched out of the steel tools used in injection molding — a tedious and time-consuming process.

"With lasers, the steel surface can not only be patterned more quickly, but also with greater scope for variety," said Kristian Arntz of the Fraunhofer Institute for Production Technology IPT. "We can transfer any possible design directly from the CAD model to the tool surface: What will later become a groove in the plastic is preserved as a ridge, while the surrounding material is vaporized. The process is efficient, fully automatic and highly variable."

Engineers are now also using laser technology in engine optimization to keep friction as low as possible in order to improve efficiency. "That is true not only for the electric engines currently being developed but also for classic internal combustion engines and diesel motors, as well as transmissions and bearings," Gillner said.

Ceramic high-performance coatings are especially desirable, because they are resistant to wear yet smooth, which generates less friction. Coated metal components have until now been prohibitively expensive, having been produced in plasma chambers in which the ceramic was vaporized and applied to the surface of the components. Fraunhofer scientists have now developed a less expensive and faster method in which workpieces are coated with ceramic nanoparticles and then treated with a laser. This finishing process has already been applied to gear wheels and bearings.

Lasers can even be used to make specific modifications to the properties of engine parts. "Friction between the cylinder wall and piston is responsible for a big part of a motor's energy consumption. That is why we try to minimize it. This is especially important for engines featuring modern, automatic start-stop functions that are stressed by frequent ignition," Gillner said. "To protect them, we have to ensure that the cylinder is always coated with a film of oil. Laser technology can help reduce friction with special structuring processes that improve oil adhesion."

Laser technology is also being used to increase the efficiency and life span of electric batteries. That is good news for manufacturers and owners of electric cars, since batteries continue to be extremely expensive. The engineers and scientists at Fraunhofer are currently working on various solutions to make batteries more durable and less expensive. One approach is to increase the surface area of the electrodes with appropriate coating to increase their efficiency.

Another approach involves analyzing and optimizing production processes. Manufacturers produce batteries using one anode and one cathode cell, which they then connect. In theory that sounds pretty simple, but in practice the fusing of copper anodes with aluminum cathodes creates brittle connections that break easily. That presents a problem for application in cars that sometimes drive on cobblestone or dirt roads. With the help of lasers, researchers at the ILT have succeeded in forming durable connections between electrodes without creating the culprit brittle alloys. Researchers at the IWS have developed an alternative solution in which a laser warms the surfaces and rollers press them together.

"Using roll plating with lasers and inductive preheating, we were able to create very stable connections with high electrical conductivity, with only a minimal loss of power," Techel said. "The finished batteries are very efficient. And since only small amounts of electrical energy are transformed into heat, these batteries do not require as much cooling."